Tension pneumothorax caused by the ruptured hydatid cyst of the lung

Abstract Hydatid cyst disease puts a significant burden on the health of humans every year. The lung is the second most common organ of implantation of Echinococcus larvae. Due to the importance of early diagnosis of tension pneumothorax, this paper provides four cases of hydatid disease that presented with tension pneumothorax.


| INTRODUCTION
Echinococcosis is a parasitic infection caused by larvae of a tapeworm genus called Echinococcus. The two main species of this genus causing significant problems in humans are Echinococcus granulosus and Echinococcus multilocularis, resulting in cystic and alveolar echinococcosis, respectively. 1,2 E. granulosus is relatively more common than E. multilocularis worldwide and also in Iran; however, E. multilocularis has been reported to be fatal, demanding a deliberate diagnostic approach. 3 E. granulosus infection is endemic in China, Central Asia, South America, North and East Africa, Australia, and Eastern Europe. 4 The life cycle of this parasite consists of definitive and final hosts (dogs) and intermediate hosts (herbivores such as sheep, cattle, camel, and goats). 5 Humans are infected accidentally and are considered incidental hosts. The larvae of E. granulosus can reside in any organ with the liver followed by the lungs being the most common locations and other more uncommon sites include kidneys, brain tissue, spinal cord, spleen, pancreas, heart, adrenal glands, muscles, bones, ribs, and mediastinum. 6 Patients remain asymptomatic until the cysts are either significantly enlarged or ruptured and then the symptoms are highly dependent on the organ involved. 5 The special characteristics of the lung tissue as well as their negative pressure make them a suitable environment for the growth and placement of the cysts. 7 Pulmonary manifestations of hydatid cyst disease are cough, chest pain, dyspnea, expectoration, fever, hemoptysis, allergic reactions, and rarely anaphylactic shock. 8 The diagnostic approach to this disease includes taking a detailed history of the patient along with a complete physical examination, and after suspecting this disease, imaging modalities such as chest x-ray and CT (computed tomography) scan of the chest and abdomen should be used. All patients with pulmonary hydatid cysts should be evaluated for liver cysts. 8 Pulmonary hydatid cysts can be categorized based on their radiologic findings as small, giant, complicated, and uncomplicated. 7,8 Table 1 gives a summary of the classification.
Pulmonary hydatid cysts can lead to life-threatening complications, involving pulmonary artery embolism, pleural necrosis, pleural effusion, pneumothorax, tension pneumothorax, empyema, collapsed lung, and bronchopleural fistula. 9 The treatment of this disease includes chemical treatment with mebendazole or albendazole and surgical treatment. 10 Here we represent four cases of hydatid cysts of the lung manifesting as hydro-pneumothorax and tension pneumothorax.

| Case 1
A 16-year-old previously healthy male was admitted to the emergency department with sudden shortness of breath. Primary physical examination revealed hypotension (blood pressure = 70/50), tachycardia (pulse rate = 130), tachypnea (respiratory rate = 40), low oxygen saturation (SpO 2 = 82%), and normal body temperature. While in the emergency room, he experienced cardiopulmonary arrest therefore resuscitation and intubation were carried out for the patient. After successful resuscitation, a portable chest x-ray was done. Chest x-ray findings indicated tension pneumothorax on the right side ( Figure 1). Consequently, a chest tube was inserted to drain the excess air in the emergency department. After he gradually became more hemodynamically stable and his oxygen saturation increased (to SpO 2 = 96%) a chest CT scan was performed, which showed the classic water lily sign (detached endocyst membranes of the hydatid cyst floating in cyst fluid) ( Figure 2). The decision to do a right posterolateral thoracotomy was made. Intraoperative findings showed that the cyst membrane had fallen into the pleural space. After the removal of the membrane from the thoracic cavity, decortication was performed. The location of the hydatid cyst was detected to be in the right lower lobe and the site was then excised. After a full expansion of the right lung and removal of the chest tubes, he was discharged from the hospital with prescription of albendazole 600 mg daily.
On follow-up, he was symptom-free, and no recurrence occurred ( Figure 3). T A B L E 1 A summary of radiologic classification of the pulmonary hydatid cysts.

Classifications of hydatid cyst by radiology criteria Small Giant Complicated Uncomplicated
Features Around 1 cm >10 cm Lesion with a well-defined and smooth border Ruptured or infected Radiologic features of ruptured hydatid cyst vary from air-fluid to the water lily sign (occurring when cystic membranes float over the cystic fluid) and empty cyst sign (a fully drained cyst) F I G U R E 1 Collapse of the right lung indicating right-sided tension pneumothorax in Case 1.
F I G U R E 2 Chest CT scan of Case 1 demonstrating the classic water-lily sign.

| Case 2
An 18-year-old female with no prior medical condition was referred to the emergency department with a 2-month history of nonprogressive moderate exertional dyspnea accompanied by mild colicky pain in the epigastric area. Four days before admission, she had experienced severe pleuritic pain in the right hemithorax associated with dry cough, expectoration of salty fluid, and dyspnea which was also present at rest. Initial physical examination revealed normal blood pressure (blood pressure = 98/71), regular heart rate (pulse rate = 90), the axial temperature of 37°C, mild tachypnea (respiratory rate = 25), and absent breath sound in the right lung field. Chest x-ray findings included the total collapse of the right lung and shifting of the trachea and mediastinum to the left side; therefore, a CT chest scan was done which revealed severe hydro-pneumothorax and two hydatid cysts localized in the superior lobe of the right lung and the left lobe of the liver which measured 43 × 54 mm and 68 × 88 mm, respectively ( Figure 4). A few days after the placement of the chest tube and expansion of the lungs, with the diagnosis of a perforated hydatid cyst, the patient was a candidate for surgery. A right posterolateral thoracotomy was performed and the perforated hydatid cyst was resected. 7 days later; she was discharged in good general condition.

| Case 3
A 13-year-old boy with no underlying diseases was referred to the emergency department with the complaint of progressive intermittent dyspnea accompanied by coughing and discharge of bitter-tasting liquid from the mouth. Further history-taking revealed that 3 months prior to admission, the patient had experienced acute severe chest pain and dyspnea during playing football. Since then, his chest pain has improved, but exertional dyspnea remained. Upon arrival, the patient's vital signs were low blood pressure (blood pressure = 85/60), tachycardia (pulse rate = 130), tachypnea (respiratory rate = 30), and fever (38°C). On pulmonary auscultation, breath sounds were diminished on the left side of the chest. Chest radiography revealed the total collapse of the left lung and shifting of the trachea and mediastinum to the right side along a cyst-like lesion. Chest CT was performed and confirmed the collapse of the left lung and mediastinal shift. Based on the patient's history and imaging findings and with the diagnosis of pulmonary hydatid cyst in mind, eventually, pleuroscopy was performed which revealed the perforated cystic membranes confirming the diagnosis of pulmonary hydatid cyst ( Figure 5). The patient then underwent surgical removal of the hydatid cyst. He was put on treatment with Albendazole after surgery and was discharged a week later.

| Case 4
A 25-year-old female with no past medical history presented to a trauma center with acute dyspnea. On examination, she had hypotension (blood pressure = 85/70), tachycardia (Pulse rate = 119), tachypnea (respiratory rate = 25), and fever (38.5°C). On auscultation, no breath sounds were heard on the right side of the chest. With pneumothorax in mind, a portable chest x-ray was performed revealing collapse of the right lung and mediastinal shift to the left side confirming the diagnosis. The chest x-ray also demonstrated a cystic lesion in the lower region of the right lung ( Figure 6). Chest CT showed a collapsed right lung, a mediastinal shift to the left side, and a cystic lesion resembling a hydatid cyst with a ruptured ectocystic layer (Figure 7). A chest tube was inserted and subsequently, the patient's breathing improved a little. She later underwent surgery and intraoperative findings indicated massive destruction of the lung tissue so a complete lower lobectomy of the right lung was performed. Postoperatively her breathing improved. She was discharged after extubation and medical therapy with albendazole was continued after discharge. On follow-up, she was doing well and her chest x-ray showed no abnormalities ( Figure 8).

| DISCUSSION
Hydatid disease, as a common disease in areas with livestock, has always been a point of concern for physicians due to the complications it may have in the long term. After humans are infected with Echinococcus, this organism spreads to other organs by invading the intestinal mucosa. 8 Figure 9 demonstrates the life cycle of E. granulosus.
Pulmonary hydatid cysts as well as cysts in any other organs remain asymptomatic until enlarged or ruptured. Rupture in lung cysts may occur due to any condition leading to a rise in pulmonary or intra-abdominal pressure. 11 Tension pneumothorax is a rare complication of the pulmonary hydatid cyst and if acute it can manifest as severe  dyspnea, tachycardia, tachypnea, jugular vein distention, and hypotension with unilateral diminished lung sounds, and trachea-mediastinal shift to the opposite side. 11 In our cases, symptoms such as intermittent dyspnea which had gradually worsened over time, accompanied by cough and expectoration of salty fluid, along with the hydatid disease being endemic in our region led us to suspect hydatidosis as the cause. In all four of our patients, pulmonary sounds were unilaterally absent. Examination and imaging findings indicated massive hydro-pneumothorax and tension pneumothorax. Imaging modalities such as CT scan and chest x-ray were of great help in confirming the diagnosis of tension pneumothorax and ruptured hydatid cyst. By observing the ruptured membranes and water lily sign, the diagnostic suspicion of a pulmonary hydatid cyst was confirmed. And finally, intraoperative findings demonstrated hydatid cyst as the definite cause and the pathology examination of the tissue also confirmed this diagnosis.
There have been a number of other cases of tension pneumothorax caused by a ruptured hydatid cyst in Nepal, Iraq, Israel, and Turkey 11-14 and a summary of these cases is presented in Table 2.
The initial treatment for tension pneumothorax accompanied by unstable hemodynamics is needle thoracostomy followed by chest tube insertion. When tension pneumothorax is caused by a ruptured pulmonary hydatid cyst, the main treatment is surgery with the aim of resecting the hydatid cysts without contamination of the pleural and mediastinal cavities. 11 Surgical techniques consist of enucleation (total removal of cyst), pericystectomy (removal of the first layer of the cyst), cystotomy with or without capitonnage of the pericystic space, and radical pulmonary resection. 11 Therapy with an antiparasitic agent decreases the risk of recurrence in the patients. It is recommended to prescribe a threephased treatment plan with antiparasitic agents with each phase including 6 weeks of treatment and 2 weeks of no medication. 16 In conclusion, tension pneumothorax caused by a ruptured hydatid cyst is not common. Hydatid cysts usually affect the liver, but they can also impact the lungs, which may result in serious complications such as tension pneumothorax and hydropneumothorax. As hydatid cyst disease causes a significant burden on human health, it must be considered as a differential diagnosis, especially in endemic areas, in patients presenting with dyspnea and tension pneumothorax.
Accompanying symptoms including expectorations of salty fluid and a history of blunt chest trauma prior to symptoms should be taken seriously by clinicians. Imaging assessments including chest x-ray and CT scans are helpful. Treatment of a ruptured lung hydatid cyst causing tension pneumothorax is mainly surgery. Therefore, it is crucial to gather a comprehensive medical history and determine the underlying cause of pneumothorax, as the management of hydatid cyst-induced pneumothorax differs from other causes. Additionally, patients require antiparasitic treatment to prevent a recurrence.